1. Field of the Invention
The invention is directed to a device for identifying fingerprints by use of ultrasound having an electronic evaluating circuit, a body which is filled with liquid and has a supporting surface with a plane outer side for the fingerprint to be analyzed, an ultrasonic transmitter and ultrasonic receiver, and is used for identifying fingerprints as means for authorizing access for persons to technical systems, rooms, vehicles, etc.
The invention serves in particular to replace PIN numbers used in connection with banking cards or other authorization identification. Accordingly, the invention can be applied in such areas as
use of automatic tellers and the like by means of banking cards PA1 monitoring access to rooms and buildings by means of authorization cards PA1 authorized use of computing devices, motor vehicles, etc. PA1 An ultrasonic hologram is generated and implemented in a card. PA1 Human skin is exposed to ultrasonic radiation to detect a fingerprint, the ultrasonic radiation in its entirety or in part, depending upon the concrete arrangement, is directed onto the hologram. PA1 The occurring interference patterns of the (coherent) ultrasonic waves can be used for identification, for example, by way of correlation analysis. PA1 the identification process is relatively stable in the face of environmental influences (e.g., small surface-area disfigurement or soiling of the examined skin region) due to the holistic character of feature detection; PA1 deep skin regions (epithelial layer) are also included in feature detection so that it is relatively forgery-proof; PA1 due to the physical properties of ultrasonic waves, the amount of wave amplitude as well as its phase can be utilized for feature detection so as to increase reliability of identification.
2. Description of the Related Art
There are a number of known commercially available technical solutions which are based on graphical comparison of the skin surface of the finger with reference patterns stored in computer memory. For this purpose, the fingerprint to be analyzed is photographed by a pixel-oriented optoelectronic camera (e.g., a CCD matrix camera), the measured values are convened in an analog-to-digital converter or ADC and entered in an electronic computer in which they are compared with reference images, e.g., based on the patterns of the fingerprint, which are stored in the computer memory.
A process and an arrangement using ultrasonic waves for analyzing fingerprints instead of photo-optical (imaging) elements is known from DE-OS 36 10 397, wherein the following possibilities were considered:
The application of ultrasonic waves as described above has the following advantages:
Further, it is obviously possible to realize devices on the basis of ultrasound which are smaller, more robust and less expensive than devices based on optical, graphical comparisons.
An arrangement in which a quantity of individual elements arranged in matrix form is provided as ultrasonic transmitter and/or ultrasonic receiver is described in DE-OS 40 16 105 "Process and Arrangement for Determining Surface Structures". The individual transmitter elements are preferably actuated successively in time in a pulsed manner. In this type of operation, the transmitter matrix and the receiver matrix can be identical and the individual elements are operated optionally as transmitters or receivers via a measuring point change-over switch. Further, it is obvious that the matrix form can be substituted by arranging pairs of transmitters and receivers on a scanner.
Based on the laws of Fourier transforms, it is obvious that the individual receiver signals in such an arrangement are not invariant with respect to rotation of the fingerprint on the supporting surface.
Moreover, since the received signals are (complex) sound amplitudes in analogous Fourier transforms with the use of ultrasound, the receiver signals also depend on the positioning of the fingerprint (multiplicative linear phase function corresponding to the displacement rule of Fourier transforms).